Method of recovering fatty acids



Aug. 29, 19?9.` o. M. URBAIN AET Al. 2,171,198 METHOD oF'REoovERINGFATTY Aolps Filed Feb. 1s, 1957 Maf/vif@ Patented Aug. 29, 1939 BIETHODF RECOVERING FATTY ACIDS Oliver M. Urbain and William R. Stemen,Columbus, Ohio, assignors to Charles H. Lewis, Harpster, OhioApplication February 13, 1937, Serial No. 125,666

Claims.

This invention relates to a process for recovering fatty acids fromsolutions containing the same. In its more specific aspect, theinvention contemplates the recovery of the fatty acids pres- 5' ent inthe soaps discharged in waste Waters from laundries and the like.

It is well-known that the wash waters or suds employedlin launderingoperatio-ns contain from 0.25 gram to 5.0 grams of fatty acids perliter.

l0 These fatty acids are, of course, present in the form of sodium andpotassium salts, that is, in the form of soaps. In addition to soaps,the laundry wastes contain so-called soap builders,

free alkali, dirt, dyes, greases, starch, carbohy- 15 drates, lint, andother cellulosic materials as well as various forms of bacteria.

The present process is primarily concerned with the steps of freeing thefatty acids from the soaps and recovering the same from the waste solu-20 tion. The fatty acids may be released from the soap by effectinghydrolysis thereof through the addition of a dilute acid such as dilutehydrochloric to the waste.

`When dilute hydrochloric acid is added to 25 laundry Waste or the like,the fatty acids are released from the soaps according to the followinggeneral reaction:

R.COO.Na-l-IICl- R.COOH-l-NaCl Soap Fatty acid A specific example of thegeneral reaction above is given as follows:

0171135.COO.Na-}HCl- C1'zI-I35.COOH|NaCl Sodium stearate Stearic acid 35The above reactions take place at all pHs below pH 7.0, but even atpI-Is above pH '7.0 the soaps hydrolyze according to the followinggeneral reaction: f

40 Soap Fatty acid It should be noted that this reaction is of thereversible type. If the fatty acid formed on the right is removed, thehydrolysis of the soap will 45 proceed to completion. In other words, aslong as the pressure is eliminated from the right side of the reaction,it will continue to move to the right.

A specific example of the hydrolysis of a soap 50 is given in thefollowing reaction:

Sodium palmitate Palmitic acid Coming now to a description of thepresent process, reference will be had to the accompany- 55 ing drawingfor clarification, wherein:

.Figure 1 is a diagrammatic flow chart representing thevarious steps inthe process; and

Figure 2 is a more or less diagrammatic illustration of a suitablefilter structure for employment in removing the fatty acids.

Referring to the drawing, the Waste containing the recoverable fattyacids is first passed through a screening unit to free the same ofentrained solids and thence preferably passed through a coarse sandfilter to remove such solids as might otherwise foul the subsequentchemical lter unit. 'I'here is added tothe Waste a dilute acid, such ashydrochloric acid, to induce hydrolysis of the contained soaps. Thesolution is then passed into a filter for removing fatty acids.

The filtering medium employed in the filter is of considerableimportance in the present invention. It comprises a more or lesschemically inert carrier in the form of granular coke or magnesiasilicate brick impregnated with Vzinc oxide. In the present process thezinc oxide is the active reagent in the removal of the fatty acids. Zincoxide has a solubility of 0.001 gram in 100y cc. of Water at 20 C. atthe saturation point so that Very little of the reagent Will be lostupon passage of the waste through the chemical filter. The filteringmedium is preferably employed as a granular mass, theindividual granulesof which Vwill pass a five-mesh screen and be retained on a twentymeshscreen. The carriers are unreactive chemically and withstand hightemperatures Without affecting their physical structures. Additionallythey are inexpensive and produced in almost unlimited quantities.

To obtain the filtering medium, that is, the carrier, impregnated withzinc oxide,`the carrier is pickled in a saturated solution of zincnitrate or zinc chloride until the granules of the carrier becomethoroughly saturated with the reagent. The excess reagent is then drawnoff and the granulated mass dried in a current of warm air, say, at atemperature of around 120 C. After drying, the material is ignited at atemperature ranging from 600 C. to 900 C. At this temperature the zincnitrate or the zinc chloride will be converted to zinc oxide. Regardlessof the source from which it is derived, the active reagent is Zincoxide. l

When awaste solution containing fatty acids is passed over thismaterial, the following reaction will take place:

Fatty acid Zinc salt of fatty acid From the above reaction it is seenthat there is formed on the surface of the granules in the chemicalfilter a zinc salt of the fatty acids'. When the material has becomeexhausted, it can be regenerated and the fatty acids released by passingsuperheated steam through the material. The reaction is as follows:

Zn(OOCR) 2+H2O=ZnO+2R-COOH Zinc salt of Steam Fatty acid fatty acid Itshould be noted that the first reaction is dependent upon the speed ofthe hydrolysis of the fatty acid salts, but since We are removing thefatty acids as fast as they are released by hydrolysis, the hydrolysisreaction proceeds with f, great rapidity and the whole procedurerequires less than fifteen minutes, provided of course that the ZnO isat all times in excessr of the fatty acid content.

The second reaction is complete Within a few minutes time as hot steambreaks down the zinc salts of the fatty acids very readily andveryeasily. The steam which is introduced into the chemical filter carriesover with it the fatty acids, thus functioning to remove the same fromthe filter and regenerate the latter. The steam carrying its fatty acidcontent is passed to a suitable condenser, and the condensate is thencedelivered to a conventional evaporating unit in which the water isliberated and the fatty acids recovered.

The apparatus instrumentalities employed in carrying out the process ofthe present invention are more or less conventional and relativelyunimportant to the process. It is accordingly not believed necessarythat they be specically illustrated. The screening unit is employed toremove the heavy suspended matter from the waste. Such screens areself-discharging, and the solids removed bythe screens may be flusheddirectly into a suitable sewer or the like.

The mechanical sand filter is employed to remove such suspended matteras passes the screens and to insure that no suspended matter will passinto and foul the fatty acid recovery unit. The sand filter can, ofcourse, be equipped with a conventional back-wash through the medium ofwhich it may be back-washed with clear water after each days run. rI'heback-wash water will, of course, carry the solids from the sand filterand may be likewise discharged into a suitable sewer or the like.

A suitable construction for the fatty acid recovery unit is illustratedin Figure 2 wherein the filtering chamber is designated generally at Iand constitutes a suitable sheet metal container since it is notrequired to Vwithstand excessive pressure or temperature conditions. Thecharnber I is provided with a filtering medium carrying grate 2 suitablysupported on members 3, the filtering agent diagrammatically illustratedat 6, and the line 5 through which the solution containing the fattyacids to be recovered is introduced to the filtering chamber.

The filtrate leaves the bottom of the chamber through the line 6 and maybe discharged through branch line 'I controlled by the valve 8 forfurther treatment or into a sewer as may be desired. A steam line 9extends into the bottom of the chamber I and is provided with aperforated extension I for delivering steam below the filtering mediumfor the purpose of driving off the fatty acids from the filter. Thesteam carrying its fatty acid content leaves the top of the filterthrough line I I controlled by valve I2 and passes to the condenser I3.The condensate is then delivered through line I4 to a suitableevaporating unit I5 wherein the water is driven off through the line I6and the fatty acids are recovered.

Oftentimes during the introduction of steam to the filtering chamber I,condensation occurs inthe filtering medium, and the condensate carryingsome of the fatty acids passes out through the line 6. In this case thevalve 8 can be closed and this condensate passed through the by-passline Il' controlled by the valve I8 and introduced to the line I4 toflow with the condensate from the condenser I3 to the evaporator I5.

It will be understood that the process is not dependent upon thisparticular form of apparatus, nor is the invention to `be limited by theforegoing description beyond the scope of the subjoined claims.

Having thus. described our invention, what We claim is:

1. In a process for the recovery of fatty acids from solutionscontaining the same, the step comprising effecting chemical removal ofthe fatty acids by passing the solution through a lter charged withzincoxide and thereafter effecting recovery of said fatty acids by treatmentof the zinc oxide filter.

2. A process for the recovery of fatty acids from solutions containingthe same, comprising effecting chemical removal of the fatty acids bypassing the solution through a filter charged with zinc oxide,thereafter passing steam therethrough to free the fatty acids from thefilter and carry them over to a condenser, and finally evaporating thewater from the condensate and recovering the resulting fatty acids as aproduct of the process.

3. A process for recovering fatty acids from soap solutions comprisingadding a dilute acid lto the soap solution to release the fatty acidsfrom the soap by hydrolysis, passing the solution through a filtercharged with zincoxide to chemically remove the fatty acid product V ofthe hydrolysis reaction, and finally recovering the fatty acids from thefilter.

4. A process for recovering fatty acids from laundry Waste comprisingadding to the waste a quantity of I-ICl to effect hydrolysis of the soapsolution and release of the fatty acids, chemically removing the fattyacids as released by effecting the hydrolysis in the presence of a -zincoxide carrying reagent, and nally recovering the fatty acids from saidzinc oxide carrying reagent.

5. In a process for recovering fatty acids from solutions containing thesame, the step comprising effecting chemical removal of the fatty acidsby passingthe solution through a filter composed Vof substantially inertgranular material impregnated with zinc Voxide and thereafter effectingrecovery of said fatty acids by treatment of the zinc oxide filter.

OLIVER M. URBAIN. WILLIAM R. STEMEN.

